The invention relates to a sintered composite material as the contact material for medium-voltage vacuum power circuit breakers, particularly in the switching voltage range from 7.2 kV to 36 kV, consisting of a burn-off-resistant metal component having a melting temperature in the range between the melting temperature of copper (1083.degree. C.) and 2000.degree. C., for example, iron, cobalt, chromium, nickel, zirconium or alloys or mixtures of these metals.
The contact materials for medium-voltage vacuum power circuit breakers must meet stringent requirements as to current interrupting capacity (currents of at least 8 kA) and burnoff resistance (more than 10,000 switching cycles at nominal current). In order to assure the required interrupting power (nominal voltage times short-circuit current), the participating material components must have melting points below 2000.degree. C., since metals with higher melting points have an increasing tendency toward secondary electron emission, which unduly limits the switching capacity (power interruption). In order to ensure the desired switching frequency, it is known to use as the burnoff-resistant components metals with a melting point above the melting temperature of copper (1083.degree. C.). In order to avoid refiring of the switching tube after the zero current crossing when the voltage reappears, it is necessary, as is well known, that the metal vapors produced in the switching arc are condensed sufficiently rapidly. The metals used heretofore for lowering the breaking currents such as, for instance, bismuth, tellurium, selenium, manganese, lead and zinc, are not suited for vacuum switches of the order of magnitude above-mentioned.